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Kim, Gwanho,Kim, Wuseok,Lee, Sanghee,Jeon, Sangmin Elsevier 2019 Sensors and actuators. B Chemical Vol.288 No.-
<P><B>Abstract</B></P> <P>We investigated the impact dynamics of droplets containing various sizes and concentrations of polystyrene microparticles (PSM) on superhydrophobic surfaces using a high-speed camera and a quartz crystal microresonator (QCM). Gold nanoflake structures were synthesized on QCM surfaces and treated with perfluorooctane ethylthiol molecules to obtain superhydrophobic characteristics. Upon the collision onto the superhydrophobic surface, the droplet spread, retracted, and bounced off the surface due to its nonwetting characteristics. Within the experimental range of PSM size and PSM concentration, the high-speed camera detected only negligible changes in the impact dynamics; however, abnormally large changes in the resonance frequency were observed with the QCM when the concentration or sizes of the PSM exceeded a certain threshold. The abnormal change in frequency was attributed to the formation of a shear-induced PSM structure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> QCM was employed to investigate the impact dynamics of PSM suspension droplet. </LI> <LI> Exceeding a certain threshold induced abnormally large change in resonance frequency. </LI> <LI> The abnormal change in frequency was attributed to the shear-induced PSM structure. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Gwanho Kim,Donghyun Yi,Jongeun Yim 물리치료재활과학회 2021 Physical therapy rehabilitation science Vol.10 No.3
Objective: The purpose of this study was to investigate the effect of sprinter pattern bridging exercise using theraband on activation of lower extremity and abdominal muscle and to find out postures that can effectively improve abdominal and lower extremity muscle strength and increase abdominal stability. Methods: This study was designed as a cross-sectional study. The following research was done with applicants attending S university in Seoul to compare the difference in muscle activity between one-leg-Support bridging exercise and sprinter-pattern bridging exercise using theraband. For 48 study participants, we first measured their MVC. Then, we applied one-leg-support bridging exercise and sprinter-pattern bridging exercise at random order. These data were expressed as the percentage of maximal voluntary contraction (%MVC).Electromyography analysis was performed by measuring the external obliques, internal obliques, biceps femoris, and gluteus maximus. Results: There was a statistically significant increment of muscle activity in external and internal oblique muscle(p<0.001)by sprinter-pattern bridging exercise using theraband. On the lower body, statistically significant increment of muscle activity in biceps femoris and gluteus maximus was found(p<0.05). On the other hand, on erector spinae, there was statistically significant decrease in muscle activity(p<0.05). Conclusions: Efficient treatment is expected when sprinter-pattern bridging exercise using theraband is applied clinically.For patients with chronic knee and ankle pain who have difficulty bearing weight, including low back pain and internal rotation of the femur, starting with a low weight bearing, we think it will be helpful in planning systematic training aimed at progressively strengthening the lower extremities.
김관호(Gwanho Kim) 한국언론학회 2012 한국언론학보 Vol.56 No.6
Survival audition program, ‘I am a singer’ Season 1, aims for full-scale music program through touching the heart of the audience. Competing narratives included by the element of fun in this program, however, had been used for decades as a way television to exercise power to popular music and then abolished recently. While the narratives of the competition for musicians can be found from examples of the Western modern music, this program stands for a phenomenon of transforming and spreading such ideology of the Western music to the 21st-century version of Korea. This study has the objective to study the diffusion mechanism of competing narratives and unfold its implications on the TV program ‘I am a singer’ on the basis of the recognition of Adorno’s critical theory. First of all, we identify the power advantage of the willingness to restore the television through a dialectical relationship between popular music and television for 50 years. And we examine the standardization and plugging cases and their implications as the ideology devices hidden in the program. However, the public who have the critical comments on the music contest program give up the criticism and fall into frustration due to the social atmosphere and decentralized listening attitude. This recognizes the limits of the public isolated by an individual in the capitalist society.
Facile Nanocasting of Dielectric Metasurfaces with Sub-100 nm Resolution
Kim, Kwan,Yoon, Gwanho,Baek, Seungho,Rho, Junsuk,Lee, Heon American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.29
<P>This work presents a facile nanocasting technique to fabricate dielectric metasurfaces at low cost and high throughput. A flexible polymer mold is replicated from a master mold, and then the polymer mold is used to shape particle-embedded UV-curable polymer resin. The polymer mold is compatible with flexible and curved substrates. A hard-polydimethylsiloxane improves mechanical stability of the polymer mold providing sub-100 nm patterning resolution. The patterned resin itself can work as a metasurface without secondary operations because dielectric particles sufficiently increase the refractive index of the resin. The absence of the secondary operations allows our method to have higher productivity and cost competitiveness than those of typical nanoimprint lithography. Experimental demonstration verifies the feasibility of our method, and the replicated metasurface exhibits a conversion efficiency of 46% in the visible, which is comparable to metasurfaces based on low-loss dielectrics. Given that conventional dielectric metasurfaces have been fabricated by electron beam lithography at formidable cost due to low throughput, our method will be a promising nanofabrication platform and thereby facilitate commercialization of dielectric metasurfaces.</P> [FIG OMISSION]</BR>
Electrically tunable metasurface perfect absorber for infrared frequencies
Yoon Gwanho,So Sunae,Kim Minkyung,Mun Jungho,Ma Ren-Min,노준석 나노기술연구협의회 2017 Nano Convergence Vol.4 No.36
We theoretically investigate a metasurface perfect absorber based on indium-tin-oxide as active material. Our design scheme relies on conventional metal–oxide–semiconductor model and the Drude model. Inducing a voltage into the device causes a blue-shift of 50 nm in the reflectance spectrum in the infrared region. The total thickness of the device is only 3.5% of the working wavelength λ = 2.56 μm, and the rate of reflectance change reaches 5.16 at λ = 2.56 μm. Because the material that we use has advantages of easy fabrication and fast response, our design approach can be used for numerous applications on active plasmonic sensors and filters.
Complete amplitude and phase control of light using broadband holographic metasurfaces
Lee, Gun-Yeal,Yoon, Gwanho,Lee, Seung-Yeol,Yun, Hansik,Cho, Jaebum,Lee, Kyookeun,Kim, Hwi,Rho, Junsuk,Lee, Byoungho The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.9
<P>Reconstruction of light profiles with amplitude and phase information, called holography, is an attractive optical technology with various significant applications such as three-dimensional imaging and optical data storage. Subwavelength spatial control of both amplitude and phase of light is an essential requirement for an ideal hologram. However, traditional holographic devices suffer from their restricted capabilities of incomplete modulation in both amplitude and phase of visible light; this results in sacrifice of optical information and undesirable occurrences of critical noises in holographic images. Herein, we have proposed a novel metasurface that is capable of completely controlling both the amplitude and phase profiles of visible light independently with subwavelength spatial resolution. The full, continuous, and broadband control of both amplitude and phase was achieved using X-shaped meta-atoms based on the expanded concept of the Pancharatnam-Berry phase. The first experimental demonstrations of the complete complex-amplitude holograms with subwavelength definition at visible wavelengths were achieved, and excellent performances with a remarkable signal-to-noise ratio as compared to those of traditional phase-only holograms were obtained. Extraordinary control capability with versatile advantages of our metasurface paves a way to an ideal holography, which is expected to be a significant advancement in the field of optical holography and metasurfaces.</P>